1. Field of the Invention
The invention is directed to a hydrodynamic torque converter with a hydraulic converter circuit having at least a pump wheel and a turbine wheel, wherein each of these wheels has a blade arrangement forming flow chambers. A stiffener is disposed at a free end of each of these blade arrangements between the pump wheel and the turbine wheel. The stiffeners form part of a toroid. A choke element is mounted in the toroid and movable by a predetermined depth into the associated blade arrangement to regulate the through-flow cross section for the hydraulic fluid of the converter circuit which is connected via a line system to a supply arrangement.
2. Description of the Related Art
A prior art hydrodynamic torque converter having an impeller or pump wheel and a turbine wheel is disclosed in German reference DE-PS 884 141. Each of these wheels has a blade arrangement to form flow chambers, a rib or stiffener being formed at the free end of the blades. The stiffeners, together with a stiffener on the stator or guide wheel side, form a toroid.
According to FIG. 1 of the prior art reference, a choke element which slides into the flow path between the pump wheel and turbine wheel is displacably arranged on the driven shaft of the torque converter. A spring urges the choke element into a position in which it exercises its fill choke effect. The purpose of this choke element is close the converter circuit while the driving engine is being started and to switch the converter circuit on only after a determined rate of rotation of the engine has been reached. The opening of the converter circuit occurs automatically when, after reaching an adequate rate of rotation of the driving engine, a sufficient pressure has built up in the converter circuit to remove the choke element from the flow path between the pump wheel and turbine wheel against the action of the spring. The switching may occur suddenly if the spring has a very low rigidity; but the spring may also be selected enabling the adjustment of the choke element to determined intermediate position at a rate of rotation of the engine, wherein the choke element is partially moved into the flow path between the pump wheel and turbine wheel. In this way, the starting torque of the torque converter is adapted to the torque characteristic of the driving engine, so that problems with cold starting of diesel engines, for example, can be countered by changing the converter characteristic.
However, a problem with the prior art torque converter shown in FIG. 1 of the above-cited German patent is that it requires an enormous amount of axial space because the pump wheel and turbine wheel, choke element and spring are arranged next to one another axially and because the choke element must be allowed an axial displacement path corresponding to the depth to which this choke element penetrates into the flow path between the pump wheel and turbine wheel because only in this case can this flow path be either fly closed or fully opened. Since the axial installation space available for the torque converters is constantly being reduced in modern vehicles, especially in small trucks, the torque converter known from the above-cited patent is absolutely unsuitable for serial manufacture.